The Roanoke Valley SPCA holds clicker training classes to make dogs more adoptable, and get a nice write-up in the Roanoke Times:
[Merope Pavlides] said owners can learn how to clicker train their own dogs. "The most important thing and the thing that takes the most practice is timing, so that the click marks precisely as the behavior is wrapping up."
Sometimes it can be just a split-second difference. For instance, if the dog sits down, turns its head and then it hears a click, it will think it needs to turn its head every time to get the treat.
Returning to Lilly, the canine already knows how to sit. But Pavlides wants Lilly to remember how she got the treat the last time and what she must do to get it again.
Lilly tries jumping up, but the trainer just pulls the treat away. Then the dog reaches up and paws Pavlides' arm. Again, no treat. It's not until Lilly displays the correct behavior that she hears the click and gets the treat. The next time around, Lilly sits more quickly.